The present invention relates to a mechanism for adjusting the height of the back support of a chair, and particularly to simultaneously adjusting the height and horizontal position of the back support under the constraint that the back support always stands vertically. According to a sitter""s need, the back support can support the sitter""s back or waist by adjusting the back support to a suitable height.
The conventional mechanism for a height adjustable chair back support is mainly a mechanical structure between a chair seat and a chair back support by which the position of the back support can be changed. The conventional high adjustment mechanism has the following disadvantages. First, the mechanical structure consists of many parts; therefore, the composition of the structure is time-consuming. Secondly, having many parts leads to a structural complexity that makes the coupling of the parts less reliable. Moreover, the conventional mechanism of adjusting height of a back support is realized by rotating a screwed rod by turning a spherical knob fixed at one end and thus driving an axle beam at the other end. Restricted by the diameter of the screwed rod, this process is slow and inconvenient to modern people.
Accordingly, the primary object of the present invention is to provide a mechanism for adjusting the height of the back support of a chair, which comprises a frame, a back support, a first link, and a second link. The frame has two lateral plates extending vertically at the top thereof, which lateral plates have two pairs of pivot holes formed in corresponding positions. A U bracket is mounted on the rear wall of the back support, whose lateral plates have two symmetrically formed pairs of axle holes. Two ends of the first and the second links are respectively pivotably connected to the U bracket and the frame by using axle pins passing through those pivot and axle holes. While those links are rotating about the top of the frame, the back support always stands vertically. When the links are placed vertically, the back support is in a higher position. When the links are placed horizontally, the back support is in a lower position.
As a further object, the present invention provides a multiple-step positioning of the back support of a chair through allowing a stepwise rotary motion of the first and second links, ranging from zero to ninety degrees. Therefore, a chair with the mechanism is suitable for sitters of various ages.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing.